Liquid jet recording apparatus using a fine particle dispersion recording composition

ABSTRACT

In an apparatus producing a high-quality and high-resolution image having high water and light resistances with an orifice having a diameter less than φ25 μm (less than 500 μm 2  in terms of cross-sectional area of the orifice) by use of a fine particle dispersion recording composition, nozzle clogging can be prevented. A recording is accomplished by a liquid jet recording apparatus for ejecting a recording composition including dispersed fine particles from a small orifice toward a receiving medium, wherein a size D p  of the fine particles and a diameter D o  of the small orifice are determined by a relationship 0.001≦D p /D o ≦0.01.

This is a continuation of application Ser. No. 09/360,996, filed Jul. 8,1999, now U.S. Pat. No. 6,338,545.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a liquid jet recordingapparatus and, more particularly, to a liquid jet recording apparatususing a recording composition where fine particles are dispersed.

2. Description of the Related Art

Recently much attention has been paid to a non-impact recordingtechnology because the noise caused by its recording operation can bereduced to an almost negligible degree. Among this technology, anink-jet recording method, which is capable of high-speed recording, is apromising candidate, and its operation can be performed using a plainpaper without a special fixing process. In this field, variousapproaches for practical use have been proposed including those alreadycommercialized and others still in the development stage.

Such an ink-jet recording method, where droplets of a recordingcomposition, usually called ink, produces a recording image on a recordreceiving member by flying droplets of a recording composition directlyonto a surface of the record receiving member. This recording system canbe classified into several processes according to the methods ofgenerating the droplets and controlling the flight direction of thedroplets.

In the prior art, for example in U.S. Pat. No. 3,060,429, it is knownthat a Teletype process, which is an electrostatic attraction typeprocess, provides a generation of droplets of a recording composition byelectrostatic pull, and the resulting droplets can be controlled by anelectrical field according to recording signals to place the droplets ona surface of a record receiving member selectively to achieve arecording.

U.S. Pat. Nos. 3,596,275 and 3,298,030 describe a Sweet process which isa continuous stream and charge-controlled type process, in whichdroplets can be generated by a continuous vibration method, with anelectrostatically controlled charge, and then the droplets pass betweena pair of electrostatic deflecting electrodes with a uniform electricfield to deposit the droplets on a surface of a record receiving member,thus producing a recording image.

As another method, for example, U.S. Pat. No. 3,416,153 teaches a Hertzprocess, in which an electric voltage is applied between a nozzle and aring-shaped electrode near the front of the nozzle to generate a mist ofliquid droplets by continuous vibration to obtain a recording image on arecording member. That is to say, in this process a strength of theelectric field applied between the nozzle and the electrode can bemodulated in accordance with recording signals to control a mist stateof the droplets, thereby creating a gradation in the recording image.

Moreover, as another method, for example, U.S. Pat. No. 3,747,120discloses a Stemme process. A principle of this process is fundamentallydifferent from that used in the above three processes. That is, whileall the above three processes employ electrical control of the dropletsemitted from the nozzle during the flight from the nozzle to place thedroplets corresponding to the recording signals on the surface of therecord receiving member selectively, in this Stemme process the dropletscan be emitted directly from the nozzle to a receiver only when they arerequired for recording. In other words, in the Stemme process,electrical recording signals can be applied to a piezo vibrating elementwhich is attached to a recording head with the nozzle, in which therecording liquid can be emitted, to convert the electrical signals to amechanical vibration of the piezo element. The droplets can be emittedfrom the nozzle according to the mechanical vibration, thereby forming arecording image on the record receiving member. This process is called adrop-on-demand type.

Furthermore, Japanese Patent Publication 56-9429 discloses still anotherprocess previously proposed by the present applicants. This process alsoemploys the so-called drop-on-demand method which emits and fliesdroplets of a recording composition from the nozzle according torecording signals. This process is a so-called bubble-jet method whereink droplets can be ejected from the nozzle by an action of a vaporbubble in an ink generated by heating the ink in an ink chamber.

As noted above, although the ink-jet recording method has variousprocesses on the basis of the principle, there is a common point betweenthese processes, in which common point droplets of a recordingcomposition, generally called ink, are emitted to form the recordingimage on the record receiving member. Such ink is generally an aqueousrecording liquid wherein a water-soluble dye is dissolved. Recently,however, due to a strong need for water and light resistances inrecorded images, it has been anticipated that a pigment-based ink with astrong image durability will be used as a color agent for the recordingcomposition of ink-jet recording ink. For example, aqueous pigment-basedinks for ink-jet recording ink which meet a basic demand for recordingquality, ejection characteristics, storage stability, penetration andabsorption properties into a recording medium and the like, aredescribed in Japanese Laid-Open Publications 2-255875, 4-57859, and4-57860. However, the pigment-based inks described in the abovepublications have an inherent disadvantage of particle dispersioninstability in a liquid medium, unlike the dye which can be dissolved inthe liquid medium stably, thus creating problems, such as pigmentaggregation, sedimentation, separation in the recording liquid andthereby nozzle clogging which plague ink-jet recording technology.

On the other hand, to obtain a high-quality and high-resolution ink-jetrecording image, a smaller nozzle has been required for this purpose,although a conventional nozzle diameter from φ33˜φ34 μm (about 900 μm²in terms of cross-sectional area of a nozzle orifice) to φ50˜φ51 μm(about 2000 μm² in terms of cross-sectional area of the nozzle orifice)in a recording head has been used. In this case, when the recordingcomposition wherein the aqueous dye can be dissolved is used as anink-jet ink, the problem of nozzle clogging is resolved because the dyeis dissolved completely in the liquid medium. For the pigment-based ink,however, there has been a serious problem of nozzle clogging in arecording operation with the smaller nozzle having, for example, anozzle diameter of less than φ25 μm.

Furthermore, the above recording composition including the pigments cancause an ink passageway of the ink-jet recording head to be cut away anddamaged due to a long time operation, in the same way that a mountaincan be eroded by river water including small pebbles. Although it is nota problem when only the ink passageway is subjected to slight damage andwear, damage and wear of the orifice of the nozzle lead to seriousdegradation of ink drop ejection characteristics.

Especially, because a smaller ink drop volume is required to achieve ahigh-quality and high-resolution ink-jet recording image in the ink-jetrecording method, the nozzle diameter of the recording head has becomeincreasingly small. For example, the nozzle diameter has become lessthan φ25 μm, or less than 500 μm² in terms of cross-sectional area ofthe nozzle orifice, although the conventional diameter from φ33˜φ34 μm(about 900 μm² in terms of cross-sectional area of the nozzle orifice)to φ50˜51 μm (about 2000 μm² in terms of cross-sectional area of thenozzle orifice) of the recording head nozzle has been successfully used.In the conventional case, since the previous relatively large nozzle issubjected to little damage and wear, there is little influence on inkdroplet ejection characteristics, such as ejection stability, ink weightuniformity and the like, thus introducing no problem. However in thecase of the smaller nozzle having, for example, a diameter less than φ25μm, even a little damage and wear have significant influences on inkdroplet ejection characteristics, thereby introducing a serious problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid jetrecording apparatus eliminating the nozzle clogging problem, in which arecording composition formed by dispersing fine particles in the liquidis ejected from a small orifice of a nozzle to place ink droplets on areceiver medium, thus producing a recording image. Above all, thepresent apparatus is to provide no nozzle clogging problem, yet producean excellent high-resolution recording, having water and lightresistances for recorded images using a nozzle diameter of less than φ25μm (less than 500 μm² in terms of cross-sectional area of a nozzleorifice).

To accomplish the above objects, there is provided, in accordance withthe present invention, a liquid jet recording apparatus wherein arecording composition satisfies a relationship 0.001≦D_(p)/D_(o)≦0.01,where D_(p) is a size of a fine particle, and D_(o) is a diameter of afine nozzle orifice, on the condition that the diameter of the nozzleorifice is less than φ25 μm. According to the present invention, ahigh-quality recording with high water and light resistances can berealized and a reliability of an ink-jet recording apparatus can beimproved with the absence of nozzle clogging in the present recordingapparatus.

The problem of nozzle clogging in the present apparatus can beeliminated completely under the conditions that a content of the fineparticles in the recording composition is in the range of 2 to 10% byweight based on the total amount of the recording composition, and thata solid content of the recording composition including the fineparticles is less than 15% by weight, when the diameter of the nozzleorifice in the present apparatus is less than φ25 μm. According to thepresent invention, a sufficient ink density for practical use and astable dispersion of fine particles can be obtained because ofoptimization of the content of the fine particles in the recordingcomposition and the solid content of the ink, and a recorded image withhigh water and light resistances can be realized with the absence ofnozzle clogging in the present recording apparatus.

The problem of nozzle clogging in the present apparatus can be preventedcompletely under the requirement that D_(p)/t≦0.01, wherein the diameterof the nozzle orifice is less than φ25 μm, and t is a length of theorifice having a uniform cross-sectional area at an outlet portion inthe nozzle. According to the present invention, a high-quality andhigh-resolution recording image can be obtained with the absence ofnozzle clogging, thereby improving a reliability of the apparatus.

A high-quality printed image by use of the present apparatus can beaccomplished by maintaining a distance of less than 100 t from theorifice of the nozzle to a receiving medium and ejecting ink droplets ina direction of gravity.

Damage and wear of the nozzle formed of a resin in the present apparatuscan be prevented by making a hardness of the resin within a range ofRockwell M65 to M120. According to the present invention, a stablehigh-quality recording can be realized with no deterioration of the inkejection characteristic due to nozzle damage and wear.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIGS. 1A through 1D show an embodiment of a bubble-jet type recordinghead according to the present invention;

FIGS. 2A through 2G show a principle for ink drop ejection of an ink-jetrecording method;

FIGS. 3A and 3B show another embodiment of a bubble-jet type recordinghead according to the present invention;

FIG. 4 shows another embodiment which is of a multicolor ink-jetrecording head according to the present invention;

FIG. 5 shows the recording head shown in FIG. 4 equipped with an inkreservoir;

FIG. 6 shows a so-called serial printer structure in which an ink-jetrecording head of the present invention is mounted on a carriage;

FIG. 7 shows ink nozzle elements for four color inks;

FIG. 8 shows another embodiment in which four color nozzles are formedintegrally according to the present invention;

FIG. 9 shows four color recording heads filled with corresponding inkmounted on a single carriage separately;

FIGS. 10A and 10B show another embodiment in which a plurality of colorheads are stacked to form a recording head integrally according to thepresent invention;

FIGS. 11A and 11B show another embodiment in which a recording head isformed integrally with a head unit and an ink reservoir according to thepresent invention;

FIGS. 12A and 12B illustrate another embodiment, showing the unitaryhead unit shown in FIG. 11, except that only the ink reservoir is adetachable component according to the present invention;

FIGS. 13A and 13B illustrate another embodiment, showing the unitaryhead unit, except that each color ink reservoir is a detachablecomponent according to the present invention; and

FIGS. 14A and 14B show a sectional schematic view of two types ofnozzles according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First of all, although there are various processes in the ink-jetrecording method as mentioned above, a structure and a principle of theink-jet recording method used in the present invention will be describedin the following. Herein, as a representative example, a bubble-jetrecording method will be described, but rather than being limited tothis, the present invention can be applied to all ink-jet recordingmethods. Since the bubble-jet recording method, which produces a vaporbubble by heating ink, exposes the ink to severe conditions during itsoperation, that is, there is an ink heat cycle in this method, theremore likely exist technological problems producing nozzle clogging inthis method than in other ink-jet recording methods. Such technologicalproblems include deterioration of ink, promotion of a chemical reactionof the ink, and dispersion instability of pigments in the recordingcomposition. The present invention can be preferably applied to thebubble-jet recording method with exposure to such severe conditions.

FIGS. 1A through 1D show an embodiment of a bubble-jet type recordinghead according to the present invention. FIG. 1A shows a perspectiveview of the recording head, FIG. 1B shows a perspective view of a coversubstrate which is a part of the recording head, FIG. 1C shows aperspective view of the cover substrate as seen from a back side, andFIG. 1D shows a perspective view of a heating element substrate. Asshown in FIGS. 1A through 1D, the recording head includes the coversubstrate 1, the heating element substrate 2, an inlet 3 of recordingliquid, a nozzle 4, a passageway 5, a region to form a liquid chamber 6,a separate (independent) controlling electrode 7, a common electrode 8,and a heating element 9.

The cover substrate 1 can be made with the passageway 5 and the liquidchamber 6 by means of an etching method or the like on a glass substrateor a metallic substrate. The most preferable method for making the coversubstrate 1 is a plastic molding. Although a cost of manufacturing aninitial mold in this method is very expensive, the cover substrate canbe subsequently produced on a large scale, thus reducing themanufacturing cost per one article. In this case, a stable ink dropejection can be accomplished without damage and wear of a part of thenozzle 4 by selecting a hardness of the plastic as described later.

FIGS. 2A through 2G illustrate a principle for ink drop ejection of theink-jet recording method. FIG. 2A shows an equilibrium state between asurface tension of an ink 10 and an external pressure at a nozzle plane.FIG. 2B shows a microscopic vapor bubble 11 in the ink 10 generated byheating the ink 10. The heating element 9 is heated to increase itssurface temperature rapidly, and heating is continued until a boilingphenomenon occurs in the ink 10 around the heating element 9. FIG. 2Cshows an expanded state of the vapor bubble 11 which is formed byheating the ink 10 across all surfaces of the heating element 9 rapidly,so that the ink 10 nearby the heating element 9 is vaporizedinstantaneously to give a boiling bubble. At this time, a pressure ofthe ink 10 in the nozzle is increased by the expansion of the vaporbubble to give a non-equilibrium state between the surface tension ofthe ink 10 and the external pressure at the nozzle plane, and an inkcolumn 10′ then begins to expand outward from the nozzle. FIG. 2D showsthe expanded state of the vapor bubble 11 at maximum, whereby emissionof ink occurs from the nozzle, which emission corresponds to the volumeof the vapor bubble 11. Since an electric current is not supplied to theheating element 9 at this time, the surface temperature of the heatingelement 9 begins to decrease. An occurrence of the maximum vapor bubblevolume may be delayed from a time of electrical pulse application. FIG.2E illustrates a state showing the vapor bubble 11 beginning to contractfrom cooling the vapor bubble 11 with surrounding ink 10. While aleading portion of the ink column 10′ proceeds at an initial emissionvelocity, at a tail portion of the ink column 10′, a constricted part10″ is formed with a reverse flow into the ink 10 due to a decreasedpressure inside the nozzle along with the vapor bubble 11 contraction.FIG. 2F illustrates a state showing that the surface of the heatingelement 9 is cooled rapidly because the contraction of the vapor bubble11 is continued and thus the surface of the heating element 9 is coveredby the ink 10 again. Since the external pressure is higher than theinner pressure in the nozzle, ink meniscus is moved into the nozzle. Theleading portion of the ink column becomes a droplet 12 and flies at aspeed from 8 to 13 m/sec toward a receiver. FIG. 2G shows that thenozzle is refilled with the ink 10 by capillary action and the vaporbubble 11 collapses completely during a process back to the initialstate as shown in FIG. 2A.

FIGS. 3A and 3B show another recording head having an additional nozzleplate 20 attached at a tip portion of the passageway, unlike therecording head as shown in FIG. 1A. FIG. 3A shows the recording headbefore attachment of the nozzle plate 20, but FIG. 3B shows therecording head after the nozzle plate 20 is mounted. The nozzle plate 20can be formed of a resin (plastic) film, in which a orifice 21 of thenozzle plate 20 can be made by ablation with an excimer laser, or theorifice 21 can be made by a metal etching method, an electroformingmethod, a micropunching method, or the like. A hardness of materialsmust be selected to meet a required property as described later.

The foregoing discussion is of a general structure and principle of abubble jet-type recording head by use of thermal technology. As notedabove, but not limited to this, the present invention can be applied toall ink-jet recording methods.

The present invention employs a recording composition, such as recordingliquid including pigment, generally called ink, which has excellentwater and light resistances, the pigment be used as a color agent insuch ink-jet recording methods. However, when the pigment is used ascolor agent in the recording composition, stability of the pigment inthe recording composition may be deteriorated due to inadequatedispersion, unlike a dye which dissolves completely in the recordingcomposition, thus leading to problems, such as pigment aggregation,sedimentation, separation in the recording ink and nozzle clogging.Especially, nozzle clogging becomes a serious problem because ink cannot be ejected. To overcome the above problems, careful consideration isgiven to materials for the ink, a structure of the nozzle, pigmentdiameter and pigment content in the recording composition in the presentinvention. The pigment-based ink is used in the present invention. Thatis, the color agent is not the dye dissolved in water and the like, buta fine particle like pigment dispersed in the above solvent.

Furthermore, since the pigment is like an abrasive particle dispersed inthe liquid medium, the ink passageway of the recording head may besubjected to damage and wear when a tremendous amount of ink comprisingthe pigment is used, thereby leading to flaws and wear in the nozzleaffecting the ink drop ejection characteristics. To resolve theseproblems, special efforts have been directed toward optimizing ahardness of materials which constitute a nozzle component, and ink flowand pigment diameter against the nozzle size.

As a most preferable black pigment ink, for example, a black pigment,which has a neutral or basic pH, is subjected to dispersion treatment byuse of a water-soluble polymer comprising at least acrylate monomerhaving a salt of tertiary amine or a quaternary ammonium group, oracrylamide monomer. Similarly, other color pigments, such as yellow,magenta, and cyan, are also subjected to dispersion treatment by use ofan anionic polymer dispersing agent having a carboxyl group or asulfonic acid group as a water-soluble group.

Herein, a pH value of the black pigment is generally determined whenthis pigment is dispersed in pure water in a similar way to a propertymeasurement method for carbon black. When the record receiving member isa plain paper, an interfacial tension against the plain paper for blackink is higher than that for other color inks. Moreover, it is preferredthat a penetration rate into the plain paper for black ink is slowerthan that for other color inks. A high-quality image with good adhesion,good color density, and little boundary bleeding between black and othercolors can be obtained when multicolor recording is performed on theplain paper by the above inks. In addition, a vivid projection image canbe obtained when multicolor recording is performed on the recordreceiving member having transparency. An image recorded withpigment-based inks exhibits good resistance against water and light incomparison with the conventional inks based on water-soluble dyes.

The polymeric dispersing agent used in the present invention can beprepared by mainly polymerization of vinyl monomers. The resultantpolymer comprises at least the following monomer with tertiary aminesalt or quaternary ammonium moiety as a cationic monomer. Examples ofsuch vinyl monomers include N,N-dimethylaminoethyl methacrylate[CH₂═C(CH₃)—COO—C₂H₄N(CH₃)₂], N,N-dimethylaminoethyl acrylate[CH₂═CH—COO—C₂H₄N(CH₃)₂], N,N-dimethylaminopropyl methacrylate[CH₂═C(CH₃)—COO—C₃H₆N(CH₃)₂], N,N-dimethylaminopropyl acrylate[CH₂═CH—COO—C₃H₆N(CH₃)₂], N,N-dimethyl acrylamide [CH₂═CH—CON(CH₃)₂],N,N-dimethyl methacrylamide [CH₂═C(CH₃)—CON(CH₃)₂],N,N-dimethylaminoethyl acrylamide [CH₂═CH—CONHC₂H₄N(CH₃)₂],N,N-dimethylaminoethyl methacrylamide [(CH₂═C(CH₃)—CONHC₂H₄(CH₃)₂],N,N-dimethylaminopropyl acrylamide [CH₂═CH—CONH—C₃H₆N(CH₃)₂],N,N-dimethylaminopropyl methacrylamide [CH₂═C(CH₃)—CONH—C₃H₆N(CH₃)₂]. Inthe case of tertiary amine monomer, compounds which form a salt withtertiary amine include hydrochloric acid, sulfuric acid, acetic acid andthe like. Compounds which form a quaternary ammonium moiety withtertiary amine moiety include methyl chloride, dimethyl sulfate, benzylchloride, epichlorohydrin and the like. In these compounds, methylchloride and dimethyl sulfate are preferable in preparation for thedispersing agents. The above tertiary amine salts or quaternary ammoniummoieties behave as a cation in water, and exhibit a stable solubility inan acid region under neutralized conditions. A content of such monomersin copolymer is preferably from 20 to 60% by weight.

Examples of other suitable monomers constituting the above-mentionedpolymeric dispersing agent used in the present invention include2-hydroxyethyl methacrylate, acrylates having a hydroxy group and a longside chain like an ethylene oxide chain, a hydrophobic monomer such asstyrenic monomer, and water-soluble monomers at about pH 7, such asacrylamides, vinyl ethers, vinylpyrrolidones, vinylpyridines, andvinyloxazolines. Examples of the hydrophobic monomer include styrene,styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, andalkyl esters of (meth)acrylic acid. The content of a water-solublemonomer in the polymeric dispersing agent prepared by copolymerizationis preferably from 15 to 35% by weight to obtain stability of thecopolymer in water. A content of hydrophobic monomer in the polymericdispersing agent is preferably from 20 to 40% by weight to obtain a highdispersion effect of the copolymer on pigments.

Examples of carbon black pigment (C. I. pigment black 7) for black inkused in the present invention include but are not limited to #2600,#2300, #990, #980, #960, #950, #900, #850, #750, #650, MCF-88, MA-600,#95, #55, #52, #47, #45, #45L, #44, #40, ##32, #30, #25, #20, #10, and#5 (manufactured by Mitsubishi Chemical Co., Ltd.)

Examples of pigments for yellow ink used in the present inventioninclude but are not limited to C. I. Pigment Yellow 1, C. I. PigmentYellow 2, C. I. Pigment Yellow 3, C. I. Pigment Yellow 12, C. I. PigmentYellow 13, C. I. Pigment Yellow 14, C. I. Pigment Yellow 16, C. I.Pigment Yellow 17, C. I. Pigment Yellow 73, C. I. Pigment Yellow 74, C.I. Pigment Yellow 75, C. I. Pigment Yellow 83, C. I. Pigment Yellow 93,C. I. Pigment Yellow 95, C. I. Pigment Yellow 97, C. I. Pigment Yellow98, C. I. Pigment Yellow 114, C. I. Pigment Yellow 128, C. I. PigmentYellow 129, C. I. Pigment Yellow 151, and C. I. Pigment Yellow 154.

Examples of pigments for magenta ink used in the present inventioninclude but are not limited to C. I. Pigment Red 5, C. I. Pigment Red 7,C. I. Pigment Red 12, C. I. Pigment Red 48 (Ca), C. I. Pigment Red 48(Mn), C. I. Pigment Red 57 (Ca), C. I. Pigment Red 57: 1, C. I. PigmentRed 112, C. I. Pigment Red 123, C. I. Pigment Red 168, C. I. Pigment Red184, and C. I. Pigment Red 202.

Examples of pigments for cyan ink used in the present invention includebut are not limited to C. I. Pigment Blue 1, C. I. Pigment Blue 2, C. I.Pigment Blue 3, C. I. Pigment Blue 15: 3, C. I. Pigment Blue 15: 34, C.I. Pigment Blue 16, C. I. Pigment Blue 22, C. I. Pigment Blue 60, C. I.Vat Blue 4, and C. I. Vat Blue 60.

Furthermore, if it is necessary to use an intermediate color such asred, green, or blue, the following pigments may be preferably used aloneor in combination. Examples of the intermediate color pigments includebut are not limited to C. I. Pigment Red 209, C. I. Pigment Red 122, C.I. Pigment Red 224, C. I. Pigment Red 177, C. I. Pigment Red 194, C. I.Pigment Orange 43, C. I. Vat Violet 3, C. I. Pigment Violet 19, C. I.Pigment Green 36, C. I. Pigment Green 7, C. I. Pigment Violet 23, C. I.Pigment Violet 37, C. I. Pigment Blue 15: 6, C. I. Pigment Blue 209.

In addition, dyes may be contained in the above color inks. Examples ofsuitable yellow dyes for yellow ink include but are not limited to C. I.Acid Yellow 11, C. I. Acid Yellow 17, C. I. Acid Yellow 23, C. I. AcidYellow 25, C. I. Acid Yellow 29, C. I. Acid Yellow 42, C. I. Acid Yellow49, C. I. Acid Yellow 61, C. I. Acid Yellow 71, C. I. Direct Yellow 12,C. I. Direct Yellow 24, C. I. Direct Yellow 26, C. I. Direct Yellow 44,C. I. Direct Yellow 86, C. I. Direct Yellow 87, C. I. Direct Yellow 98,C. I. Direct Yellow 100, C. I. Direct Yellow 130, and C. I. DirectYellow 142.

Examples of suitable magenta dyes for magenta ink include but are notlimited to C. I. Acid Red 1, C. I. Acid Red 6, C. I. Acid Red 8, C. I.Acid Red 32, C. I. Acid Red 35, C. I. Acid Red 37, C. I. Acid Red 51, C.I. Acid Red 52, C. I. Acid Red 80, C. I. Acid Red 85, C. I. Acid Red 87,C. I. Acid Red 92, C. I. Acid Red 94, C. I. Acid Red 115, C. I. Acid Red180, C. I. Acid Red 254, C. I. Acid Red 256, C. I. Acid Red 289, C. I.Acid Red 315, C. I. Acid Red 317, C. I. Direct Red 1, C. I. Direct Red4, C. I. Direct Red 13, C. I. Direct Red 17, C. I. Direct Red 23, C. I.Direct Red 28, C. I. Direct Red 31, C. I. Direct Red 62, C. I. DirectRed 79, C. I. Direct Red 81, C. I. Direct Red 83, C. I. Direct Red 89,C. I. Direct Red 227, C. I. Direct Red 240, C. I. Direct Red 242, and C.I. Direct Red 243.

Examples of suitable cyan dyes for cyan ink include but are not limitedto C. I. Acid Blue 9, C. I. Acid Blue 22, C. I. Acid Blue 40, C. I. AcidBlue 59, C. I. Acid Blue 93, C. I. Acid Blue 102, C. I. Acid Blue 104,C. I. Acid Blue 113, C. I. Acid Blue 117, C. I. Acid Blue 120, C. I.Acid Blue 167, C. I. Acid Blue 229, C. I. Acid Blue 234, C. I. Acid Blue254, C. I. Direct Blue 6, C. I. Direct Blue 22, C. I. Direct Blue 25, C.I. Direct Blue 71, C. I. Direct Blue 78, C. I. Direct Blue 86, C. I.Direct Blue 90, C. I. Direct blue 106, and C. I. Direct Blue 199. Evenin a case of using these dyes in combination, a particle diameter and acontent of pigments in respective inks must fall within the requiredrange given below.

When the above cationic water-soluble polymer is used as the dispersingagent to disperse pigments, it is preferred that pigments have anisoelectric point which is adapted to indicate more than 6, or a pH ofthe pigment as a monodispersion in pure water which characterizes thepigment is neutral or basic, for example from 7 to 10, from theviewpoint of dispersibility. It should be understood that this indicatesa strong interaction between the pigment and the cationic water-solublepolymer.

In order to obtain an aqueous dispersion where fine particle pigmentsare dispersed by use of the above materials in the present invention,the following procedures are preferably used.

(1) In a Case of Carbon Black:

Carbon black is subjected to a premixing treatment in a dispersioncontaining the cationic dispersing agent, followed by a milling processwith a dispersion device at a high shear rate. After dilution, theresultant dispersion is subjected to a centrifuge treatment to removecoarse pigments. Some materials are then added to form the desired blackink. An aging treatment may be performed, if desired. Finally, thisdispersion is subjected to a centrifuge treatment to obtain the pigmentdispersion having a desired average particle diameter. A pH range of inkprepared by the above procedure is preferably from 3 to 9.

(2) In a Case of Color Pigments other than Carbon Black:

The same procedure as for carbon black is also carried out, except foruse of the anionic dispersing agent. In a case of a serious difficultyin making an organic pigment fine, a surface active treatment can beperformed just after preparation of the pigment, or during preparationof the pigment to inhibit a crystal growth of a pigment particle. Apigment which is treated to enhance wettability is preferably used. A pHof the ink prepared by the above procedure is preferably in the range of5 to 10. From the standpoint of dispersion stability, a necessaryaverage particle diameter is preferably in the range of 0.02 to 1 μm,and more preferably 0.03 to 0.4 μm, in the case of any of black inkbased on carbon black and other color inks. Furthermore the necessaryrequirement of the average particle diameter for prevention of nozzleclogging will be described later. Additionally, a surface tension of theinks suited for the present invention is preferably in the range of 10to 60 dyn/cm.

When a recording on a plain paper with such as the above inks is carriedout, an interfacial tension of black pigment-based ink against the plainpaper is preferably high from the viewpoint of vividness of recordedcharacters. On the other hand, to reduce interdiffusion between colorinks which leads to a color bleeding phenomenon, the interfacial tensionof the color inks against the plain paper is preferably low because ahigh penetration rate into the plain paper creates a good recordingimage. Since black ink has a high interfacial tension in an acidicregion and color inks have a low interfacial tension in a basic region,black ink does not tend to spread into color inks, so that colorbleeding between black ink and color inks can be substantiallyeliminated. Herein, a value of interfacial tension between the aboveinks and the paper can be determined by a commercial dynamic wettabilitytest device based on a Wilhelmy method. A high interfacial tensionindicates that a contact angle for paper is more than 90 degrees duringa short period of 1 to a few seconds after placing an ink on the paper,a low interfacial tension means that the contact angle is less than 90degrees under the same conditions.

A dispersing agent for color inks used in the present invention is analkaline-soluble resin, and its weight-average molecular weightgenerally ranges from 1,000 to 30,000, preferably 3,000 to 15,000. Morespecifically, such resins are copolymers and salts thereof comprising ahydrophobic monomer, such as styrene, styrene derivatives,vinylnaphthalene, vinylnaphthalene derivatives, alkyl esters of acrylicor methacrylic acid, and the like, and a hydrophilic monomer, such asα,β-ethylenic unsaturated carboxyl acid, its esters of aliphaticalcohol, acrylic or methacrylic acid, maleic acid, itaconic acid,fumaric acid, derivatives thereof, and the like. Copolymers may have anyform of random, block, and graft structures, and an acid value of suchresins generally ranges from 100 to 430, preferably 130 to 360. Inaddition, examples of the dispersing agent used in the present inventionalso include water-soluble polymers or resins, such as polyvinylalcohol, carboxymethylated cellulose, naphthalenesulfonicacid-formaldehyde polycondensation product, polystyrenesulfonic acid,and the like. The alkaline-soluble polymers permit dispersion to be madeeasily and become low viscous, as compared to water-soluble polymers. Anamount of the polymer in ink, where the polymer is not attached to thepigment and dissolves in water, is preferably less than 4% by weight,although an amount of the dispersing agent can be determinedexperimentally by use of selected pigment and the dispersing agent.

It is necessary to add bases when the above dispersing agent is used inan aqueous medium. Examples of suitable bases used in the presentinvention include but are not limited to monoethanolamine,diethanolamine, triethanolamine, N-methyl-ethanolamine,N-ethyl-diethanolamine, 2-amino-2-methylpropanol,2-ethyl-2-amino-1,3-propanediol, 2-(2-aminoethyl)ethanolamine,tris(hydroxymethyl)aminomethane, ammonia, piperidine, morpholine,β-dihydroxyethylurea and other organic bases, sodium hydroxide,potassium hydroxide, lithium hydroxide and other inorganic bases. Themost suitable bases are preferably non-volatile, stable, and have a highwater-holding ability, depending upon the choice of the pigments and thedispersing agents. An amount of the bases is determined by an acid valueof the dispersing agents so that they are used to neutralize the agents.In some cases, a large amount of the bases as compared to the acid valueis often used in order to improve dispersibility, moisture holdingability, and adjust the ink pH and recording characteristics, or thelike.

Organic solvents for ink used in the present invention have excellentmiscibility with water. The organic solvents are classified into thefollowing three groups. A first group solvent has a high moistureholding ability, a non-volatile property, and a high hydrophilicity. Asecond group solvent has an organic property to some extent, a goodwettability for a hydrophobic surface, and a vaporization dryingproperty. A third group solvent which is monohydric alcohol has asuitable wettability and low viscosity.

Examples of the first group solvents include ethylene glycol, diethyleneglycol, triethylene glycol, tripropylene glycerol, 1,2,4-butanetriol,1,2,6-hexanetriol, 1,2,5-pentanetriol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, dimethyl sulfoxide, diacetonealcohol, glycerol monoallylether, propylene glycol, butylene glycol, polyethylene glycol 300,thioglycol, N-methyl-2-pyrrolidone, 2-pyrrolidone, γ-butyrolactone,1,3-dimethyl-2-imidazolidinone, sulfolane, trimethylolpropane,trimethylolethane, neopentyl glycol, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether,ethylene glycol monoallyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, triethylene glycol monomethyl ether,triethylene glycol monoethyl ether, propylene glycol monoethyl ether,propylene glycol monomethyl ether, dipropylene glycol monomethyl ether,β-dihydroxyethylurea, urea, acetonylacetone, pentaerythritol,1,4-cyclohexanediol.

Examples of the second group solvents include hexylene glycol, ethyleneglycol monopropyl ether, ethylene glycol monobutyl ether, ethyleneglycol monoisobutyl ether, ethylene glycol monophenyl ether, diethyleneglycol diethyl ether, diethyleneglycol monobutyl ether, diethyleneglycol monoisobutyl ether, triethylene glycol monobutyl ether,triethylene glycol dimethyl ether, triethylene glycol diethyl ether,tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether,propylene glycol monobutyl ether, dipropylene glycol monomethyl ether,dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether,dipropylene glycol monobutyl ether, tripropylene glycol monomethylether, glycerol monoacetate, glycerol diacetate, glycerol triacetate,ethylene glycol monomethyl ether acetate, diethylene glycol monomethylether acetate, cyclohexanol, 1,2-cyclohexanediol, 1-butanol,3-methyl-1,5-pentanediol, 3-hexene-2,5-diol, 2,3-butanediol,1,5-pentanediol, 2,4-pentanediol and 2,5-hexanediol.

Examples of the third group solvents include ethanol, n-butanol,2-propanol, 1-methoxy-2-propanol, furfuryl alcohol,tetrahydro-furfurylalcohol. The above solvents may be used alone or in acombination of two or more thereof. The content of the solvents in theink is preferably about 5 to 40% by weight.

Each aqueous pigment-based ink constituting the inks in the presentinvention may also include surface active agents, pH adjusting agents,and antiseptics, or the like. The surface active agents commerciallyavailable are helpful to prepare a color ink which has good penetrationinto the recording member, to heat the ink in the bubble-jet method, andto adjust wettability against a surface of the nozzle. To summarizeproperties of the inks formed of the above materials, it is preferredthat the black ink has a high surface tension (approximately 30 to 60dyn/cm), whereas it is preferred that the color inks have a low surfacetension (approximately 10 to 40 dyn/cm).

Using the black and color inks in the present invention, a high-qualityrecording which has no color bleeding between black and color images canbe accomplished when color recording is performed for plain papers.

When recording is accomplished with the color inks in the presentinvention, it is possible to use any of general plain paper, specialcoated paper, and plastic film for overhead projector. As mentionedabove, the ink used in the present invention can be applied to allink-jet recording methods. Above all, the inks in the present inventionare preferably suitable for an ink-jet recording method in which the inkcan be emitted by the vapor bubble generated by heating application, sothat ink droplet emission is very stable and a clear image withoutsatellite dots or the like can be provided. In this case, thermalproperties, such as specific gravity, thermal expansion coefficient andthermal conductivity or the like must be adjusted to achieve a goodrecording.

The features in the present invention will be described as follows. Asnoted above, the present invention relates to the ink-jet recordingmethod in which ink droplets can be ejected from a smaller orifice.However, nozzle clogging presents a serious problem in this method.Nozzle clogging tends to takes place when using pigment-based ink ratherthan dye-based ink, because pigment is not dissolved but dispersed inthe liquid. In addition, this nozzle clogging problem is extremely gravesince the present invention employs the smaller orifice of the nozzle ascompared to the conventional one, the present invention having, forexample, an orifice diameter of less than φ25 μm (less than 500 μm² interms of cross-sectional area of the orifice). Nozzle clogging isderived from the principle of the ink-jet recording method wherein anink droplet is ejected from a small orifice. In other words, thisproblem is due to the small orifice. The diameter of the orifice thuscorrelates closely with the size of pigment which is a so-called aliensubstance in the ink.

The present invention has focused on the sizes of the orifice andpigment, and we have discovered relationships to prevent nozzleclogging. More specifically, presence or absence of nozzle clogging wasexamined with respect to ink-jet recording using inks of various pigmentsizes and various orifice diameters for a constant period, followed byallowing the present apparatus to stand for a constant period. In thisexperiment, a partial nozzle clogging and a prior sign of nozzleclogging (slight nozzle clogging) as well as complete nozzle cloggingwere regarded as nozzle clogging.

The ink-jet recording head based on thermal energy, which recording headwas used in this experiment, is shown in FIG. 3B. FIG. 1A shows that atip of the ink passageway is the orifice of the nozzle, but the nozzleused in this experiment was covered with the nozzle plate 20 having thesame number of orifices 21 as number of nozzles 4 in FIG. 1A. FIG. 3Ashows a perspective view of the recording head before attachment of thenozzle plate 20, and FIG. 3B illustrates a perspective view of therecording head after the nozzle plate is attached. Although FIGS. 1A and3B show only four nozzles for simplicity, the actual number of thenozzles used in this experiment was 128, to give 400 dpi resolution.Other conditions for recording were as follows. A size of the heatingelement was 22 μm×90 μm, its resistance value was 110Ω, a drive voltageof ink ejection was 24 V, a width of a drive pulse was 6.5 μs, and adrive frequency was 12 kHz. Additionally, different recording heads H1to H4 having respective orifice diameter of φ25 μm, φ20 μm, φ15 μm, andφ10 μm were prepared. A thickness of each of the nozzle plate was 40 μm.

The inks used in this experiment can be formed of the followingcomposition and by the following process. The experiment was conductedusing inks with pigment diameters ranging from 0.005 μm to 1 μm incombination with the four distinct nozzle diameters of the recordingheads H1 to H4. Standing conditions after performing ink ejection for aconstant period were standing for 10 hours at a temperature of 40° C.and 30% humidity.

The process for making the inks was as follows. Using a solution wherestyrene/methacrylic acid/butyl acrylate copolymer P1 having an acidvalue of 325, the weight-average molecular weight of 11,000 and a glasstransition temperature of 84° C. was dissolved by use of potassiumhydroxide, the following carbon black dispersions D1 to D17 were made.

Materials Parts Copolymer P1 (20% by weight) 40 Carbon black MCF-88(Mitsubishi Chemical) 24 Diethylene glycol 20 Isopropyl alcohol 10 Water130

These materials was added to a batch-type longitudinal sand mill device(manufactured by AIMEX CO., LTD.) filled with glass beads, and adispersion treatment was continued for 3 hours during water cooling togive a crude dispersion with a viscosity of 17 cp and a pH of 9.6. Thisdispersion was centrifuged to remove large particles. Varying theconditions for centrifugation provided the dispersions D1 to D17 havingan average diameter ranging from 0.005 μm to 1 μm. Dilution of thesedispersions with water gave black basic ink-jet inks B1 to B17 with aviscosity of 2.5 cp, a surface tension of 45 dyn/cm, and a pH of 9.5. Asolid content of a final ink was about 7% by weight. A final amount ofpigment in these inks was 5% by weight. An average diameter of thepigment was determined by a particle size distribution measurementdevice (Otsuka Electronics Co., LTD.) using a dynamic light scatteringmethod. The average value was obtained from an initial gradient of anautocorrelation function.

In combinations of these inks B1 to B17 with the recording heads H1 toH4, nozzle clogging occurrence was examined to provide the results asshown in Tables 1 to 4.

TABLE 1 In a case of the recording head H1 (D₀ = φ25 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) D_(p)/D₀(total nozzle number) Judgment B1 0.005 0.0002 1) X B2 0.01 0.0004 1) XB3 0.02 0.0008    0/128 ²⁾ ◯ B4 0.03 0.0012 0/128 ◯ B5 0.04 0.0016 0/128◯ B6 0.05 0.002 0/128 ◯ B7 0.06 0.0024 0/128 ◯ B8 0.07 0.0028 0/128 ◯ B90.08 0.0032 0/128 ◯ B10 0.09 0.0036 0/128 ◯ B11 0.1 0.004 0/128 ◯ B120.15 0.006 0/128 ◯ B13 0.2 0.008 0/128 ◯ B14 0.25 0.01 0/128 ◯ B15 0.30.012 2/128 Δ (partial clogging) B16 0.4 0.016 5/128 Δ (partialclogging) B17 1 0.04 32/128  X (complete clogging) 1) No evaluation wasperformed due to ink instability. ²⁾ A slight instability of the ink wasobserved.

TABLE 2 In a case of the recording head H2 (D₀ = φ20 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) D_(p)/D₀(total nozzle number) Judgment B1 0.005 0.00025 1) X B2 0.01 0.0005 1) XB3 0.02 0.0010    0/128 ²⁾ ◯ B4 0.03 0.0015 0/128 ◯ B5 0.04 0.002 0/128◯ B6 0.05 0.0025 0/128 ◯ B7 0.06 0.003 0/128 ◯ B8 0.07 0.0035 0/128 ◯ B90.08 0.004 0/128 ◯ B10 0.09 0.0045 0/128 ◯ B11 0.1 0.005 0/128 ◯ B120.15 0.0075 0/128 ◯ B13 0.2 0.01 0/128 ◯ B14 0.25 0.0125 2/128 Δ(partial clogging) B15 0.3 0.015 4/128 Δ (partial clogging) B16 0.4 0.025/128 X (complete clogging) B17 1 0.05 48/128  X (complete clogging) 1)No evaluation was performed due to ink instability. ²⁾ A slightinstability of the ink was observed.

TABLE 3 In a case of the recording head H3 (D₀ = φ15 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) D_(p)/D₀(total nozzle number) Judgment B1 0.005 0.00033 1) X B2 0.01 0.00067 1)X B3 0.02 0.00133    0/128 2) ◯ B4 0.03 0.002 0/128 ◯ B5 0.04 0.002670/128 ◯ B6 0.05 0.0033 0/128 ◯ B7 0.06 0.004 0/128 ◯ B8 0.07 0.004670/128 ◯ B9 0.08 0.0053 0/128 ◯ B10 0.09 0.006 0/128 ◯ B11 0.1 0.00670/128 ◯ B12 0.15 0.01 0/128 ◯ B13 0.2 0.013 4/128 Δ (partial clogging)B14 0.25 0.0167 11/128  Δ (partial clogging) B15 0.3 0.02 27/128  X(complete clogging) B16 0.4 0.0267 52/128  X (complete clogging) B17 10.067 128/128  X (complete clogging) 1) No evaluation was performed dueto ink instability. ²⁾ A slight instability of the ink was observed.

TABLE 4 In a case of the recording head H4 (D₀ = φ10 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) D_(p)/D₀(total nozzle number) Judgment B1 0.005 0.0005 1) X B2 0.01 0.001 1) XB3 0.02 0.002    0/128 ²⁾ ◯ B4 0.03 0.003 0/128 ◯ B5 0.04 0.004 01128 ◯B6 0.05 0.005 0/128 ◯ B7 0.06 0.006 0/128 ◯ B8 0.07 0.007 0/128 ◯ B90.08 0.008 0/128 ◯ B10 0.09 0.009 0/128 ◯ B11 0.1 0.01 0/128 ◯ B12 0.150.015 6/128 Δ (partial clogging) B13 0.2 0.02 15/128 X (completeclogging) B14 0.25 0.025 44/128 X (complete clogging) B15 0.3 0.03128/128  X (complete clogging) B16 0.4 0.04 128/128  X (completeclogging) B17 1 0.1 128/128  X (complete clogging) 1) No evaluation wasperformed due to ink instability. ²⁾ A slight instability of the ink wasobserved.

From the above results, a stable ink droplet ejection in the absence ofnozzle clogging was accomplished when the pigment diameter D_(p) and theorifice diameter D_(o) satisfied a relationship 0.001≦D_(p)/D_(o)≦0.01.In this experiment, the orifice is round, but this relationship can beconverted into a modified one based on the area ratio if the orifice isa polygon.

As noted above, the ink used in this experiment was based on not dyesbut pigments which act as color agents for recording compositions. Thecontent of pigment in the ink has an important influence on nozzleclogging. To investigate the relation between the pigment content in theink and nozzle clogging, the following experiment was performed usingthe above recording head H2 (orifice diameter D_(o)=φ20 μm) and pigmentdiameter D_(p)=0.03 μm in the ink (B4), while varying the contents ofthe pigment and copolymer P1 dispersing agent as described above. Anexamination method for nozzle clogging was followed by the sameprocedure as the previous one. Table 5 shows the results.

TABLE 5 Pigment Solid (Nozzle number subjected content weight to nozzleclogging)/ (% by weight) (%) (total nozzle number) Judgment 1 3 0/128 X¹⁾ 1 6 0/128 X ¹⁾ 1 10 0/128 X ¹⁾ 1 15 0/128 X ¹⁾ 1 20 22/128  X ¹⁾ 2 30/128 ◯ 2 6 0/128 ◯ 2 10 0/128 ◯ 2 15 0/128 ◯ 2 20 25/128  X 3 6 0/128 ◯3 10 0/128 ◯ 3 15 0/128 ◯ 3 20 37/128  X 4 6 0/128 ◯ 4 10 0/128 ◯ 4 150/128 ◯ 4 20 41/128  X 5 6 0/128 ◯ 5 10 0/128 ◯ 5 15 0/128 ◯ 5 20 48/128X 6 6 0/128 ◯ 6 10 0/128 ◯ 6 15 0/128 ◯ 6 20 52/128  X 7 6 0/128 ◯ 7 100/128 ◯ 7 15 0/128 ◯ 7 20 54/128  X 8 6 0/128 ◯ 8 10 0/128 ◯ 8 15 0/128◯ 8 20 61/128  X 9 6 0/128 ◯ 9 10 0/128 ◯ 9 15 0/128 ◯ 9 20 66/128  X 106 0/128 ◯ 10 10 0/128 ◯ 10 15 0/128 ◯ 10 20 71/128  X 11 6 11/128  X 1110 58/128  X 11 15 128/128  X 11 20 1281128  X 12 6 128/128  X 12 10128/128  X 12 15 128/128  X 12 20 128/128  X 1) Low color density andimpractical.

From the results, it is preferred that the content of pigment in the inkis from 1 to 10% by weight, as a higher percentage than this range leadsto nozzle clogging. In addition to pigment content, it is understoodthat a solid content of the ink must be less than 15% by weight. In caseof pigment content of less than 1% by weight, color density is usuallytoo low to use the ink practically, although no nozzle clogging occurs.However the low density ink may be used in a combination of a pluralityof inks comprising high and low density inks. When only this lowconcentration ink is used, it is possible to supplement the densityshortage by adding an additional dye.

Other features in the present invention will be described in thefollowing. Since the recording head in the present invention can beapplied to multicolor recording, a structure of the ink-jet recordinghead for multicolor recording will be described as follows.

FIG. 4 shows another embodiment of the present invention, which is amulticolor ink-jet recording head. Referring to FIG. 4, this recordinghead is composed of a plurality of color ink nozzle elements, 31Y, 31M,and 31C, on a single common heating element substrate 30, correspondingto a plurality of colors, yellow (Y), magenta (M), and cyan (C). In thisexample and in the following examples, only three to five ink nozzleelements and nozzles for each color are illustrated, but 64 to 512elements and nozzles for each color may be provided.

FIG. 5 shows the recording head shown in FIG. 4 equipped with an inkreservoir 40 which supplies each of the Y, M, and C inks. This figureillustrates a conceptual figure comprising a recording head part and anink reservoir part constituting an ink-jet recording head of the presentinvention.

FIG. 6 shows a so-called serial printer structure in which the ink-jetrecording head of the present invention is mounted on a carriage. Thisfigure includes the ink-jet recording head 50 of the present invention,a recording paper 51, a carriage 52, guide rods 53 for the carriage, ascrew rod 54 moving the carriage, a roller 55 transporting the recordingpaper, and a roller 56 pressing the recording paper. As shown in FIG. 6,the recording head 50, which is arranged with the color ink nozzleelements 31Y, 31M, and 31C aligned longitudinally (in this figure therecording head shown in FIG. 5 is mounted vertically.), can reciprocatein an X direction in this figure in front of the recording paper 51 toachieve a recording. The recording paper is moved in a Y direction inthis figure whenever the carriage 52 is scanned (that is, moved back andforth) one time. Accordingly, a region recorded for one scan correspondsto a length of a nozzle element. Because Y, M, and C inks are arrangedin a line longitudinally, more than one scan provides a multicolorrecording image by overlapping printing regions recorded with Y, M, andC inks.

The above discussion is directed to an example showing the three colorsY, M, and C, but the present invention can be applied to a recordinghead equipped with four colors including black ink. FIG. 7 shows theabove case, wherein ink nozzle element 31B for black ink is added to thehead shown in FIG. 4.

FIG. 8 shows another embodiment of the present invention, in whichembodiment the recording head is provided with four separate color inkpaths which are made by plastic molding integrally, thereby reducingassembly cost significantly.

In general, the color ink-jet recording apparatus is composed of aplurality of color ink heads which are filled with corresponding colorinks and are mounted on a carriage 70 shown in FIG. 9. 71B, 71C, 71M,and 71Y correspond to recording heads of black ink, cyan ink, magentaink, and yellow ink, respectively. This ensures a reliability ofmeasures against nozzle clogging. For example, in a case in which therecording heads 71B, 71C, 71M, and 71Y, which are filled with thecorresponding color inks, are mounted on the carriage 70 separately asshown in FIG. 9, an initial state of a clogged recording head can berecovered easily by replacing only the clogged recording head whennozzle clogging occurs in any one of the four recording heads.

On the other hand, the recording heads which eject a plurality of colorinks, as shown in FIGS. 4 to 8, are made integrally. As noted above,taking into consideration measures for nozzle clogging, it is preferredthat the recording heads filled with corresponding color ink are mountedon the carriage separately, as shown in FIG. 9. The problem of nozzleclogging can be solved by optimizing the pigment diameter, and itscontent ratio and solid weight in the ink, as investigated in thepresent invention. Therefore, it is not necessary to mount the recordingheads filled with the corresponding color inks on the carriageseparately. The recording heads which eject a plurality of color inks,as shown in FIGS. 4 to 8, can be formed integrally in order to reduceassembly cost, realize a compact manufacture, and improve positionalprecision of color dots. Herein, the head formed integrally meansstacked recording heads 71B, 71C, 71M, and 71Y which are filled withcorresponding color inks integrally, as shown in FIGS. 10A and 10B, aswell as the recording head mounted on the single common heating elementsubstrate shown in FIGS. 4 to 8. In FIG. 10A, a single common nozzleplate 73 is provided on passageway tips 72B, 72C, 72M, and 72Y. FIG. 10Ashows a recording head before attachment of the nozzle plate 73, andFIG. 10B shows the recording head after attachment of the plate 73.Since the single common nozzle plate 73 produced by an ablationtechnique with high accuracy is assembled to form an unitary recordinghead, it is possible to improve the positional precision of color dotsas well as to reduce the manufacturing cost.

FIGS. 11A and 11B show another embodiment of a recording head of thepresent invention, which recording head is formed integrally of a headunit ejecting a plurality of color inks (the three colors of Y, M, and Cin this embodiment) and an ink reservoir part. FIG. 11A shows aperspective view of the entire recording head and FIG. 11B shows anexploded perspective view of the recording head. In these figures, therecording head comprises a head unit 100, a head chip 101, aprinted-circuit board 102, a cover plate 103, the ink reservoir part104, a stainless mesh filter 105 (105Y, 105M, and 105C), foam 106, and abottom plate 107. In this embodiment, the head unit and the inkreservoir which communicates with the head unit are divided into threeparts inside the recording head, respectively, and Y, M, and C inks canbe added to the respective parts of the ink reservoir. Since the headunit comprising a plurality of color recording heads can be constructedin a compact form, the carriage having the recording head mountedthereon can be miniaturized, thereby miniaturizing a motor driving thecarriage and realizing energy saving.

FIGS. 12A and 12B illustrate another embodiment of the presentinvention, showing the head unit shown in FIG. 11A, except that only theink reservoir is a detachable component. FIG. 12A shows a perspectiveview of the entire head unit 110 and FIG. 12B shows a perspective viewseparating the head unit 110 into a recording head part 111 and an inkreservoir part 112. Even if large quantities of inks are consumed incolor recording, reduction of an operation cost can be realized byreplacing only the ink reservoir 112. Moreover, the advantages of theunitary color head described in FIG. 11A can still be maintained.

FIGS. 13A and 13B illustrate another embodiment of the presentinvention, showing the unitary head unit, except that each color inkreservoir is a detachable component. FIG. 13A shows a perspective viewof the entire head unit 110 and FIG. 13B shows a perspective viewseparating the head unit 110 into the recording head part 111 and eachcolor ink reservoir part 112 (more specifically, 112Y, 112M and 112C).An advantage of the above structure is that an empty color ink reservoircan be individually replaced to reduce the operating cost all the more,because the Y, M, and C inks are not necessarily all consumed at thesame speeds.

As noted above, nozzle clogging is derived from the principle of theink-jet recording method wherein an ink droplet is ejected from a smallorifice. In other words, this problem is due to the small orifice.Therefore, there is a close relationship between the orifice, that is,the dimensions, geometry, and properties of the nozzle and the size ofthe pigment which is an alien substance in the ink.

In addition to the experiments mentioned above, the present inventionhas also focused on the dimensions, geometry, and properties of thenozzle and the pigment size, and we have discovered additionalrelationships to eliminate nozzle clogging. More specifically,occurrence of nozzle clogging was investigated with respect to ink-jetrecording using inks of various pigment sizes and various nozzle platethickness for a constant period, followed by allowing the presentapparatus to stand for a constant period. In this experiment, a partialnozzle clogging and a prior sign of nozzle clogging (slight nozzleclogging) as well as complete nozzle clogging were regarded as nozzleclogging.

The ink-jet recording head based on thermal energy, which recording headwas used in this experiment, is shown in FIG. 3B. FIG. 1A shows that atip of the ink passageway is the orifice of the nozzle, but the nozzleused in this experiment was covered with the nozzle plate 20 having thesame number of the orifices 21 as number of nozzles 4 in FIG. 1A.Although FIGS. 1A and 3B show only four nozzles for simplicity, theactual number of the nozzles used in this experiment was 128, to give400 dpi resolution. Other conditions for recording were as follows. Asize of the heating element was 22 μm×90 μm, its resistance value was110 Ω, a drive voltage of ink ejection was 24 V, a width of a drivepulse was 6.5 μs, and a drive frequency was 12 kHz. Additionally,recording head H5, H6 and H7 were prepared with orifices having φ25-μmdiameters and three different thicknesses t of the nozzle plate. Thethickness, t was a thickness, 40 μm for H5, 50 μm for H6, and 60 μm forH7. As noted above, there are two types of the nozzles in the presentinvention as shown in FIGS. 1A and 3B. FIGS. 14A and 14B show asectional schematic view of the two types of the nozzles. FIG. 14Aillustrates a case of attachment of the nozzle plate 20. In this case, tis a thickness of the nozzle plate 20. FIG. 14B shows that the orificeis a tip of the ink passageway. In this case, in general, there are atapered shape and a straight shape at an outlet portion of the inkpassageway. As shown in FIG. 14B, the thickness t is a length of thestraight part of the orifice having a uniform cross-sectional area atthe outlet portion.

The inks used in this experiment can be formed of the followingcomposition and by the following process. Investigation was made usinginks with different pigment diameters ranging from 0.005 to 4 μm incombination with the three distinct nozzle thicknesses t of therecording heads H5 to H7. Standing conditions after performing inkejection for a constant period were standing for 10 hours at atemperature of 40° C. and 30% humidity.

The process for making inks was as follows. Using a solution wherestyrene/methacrylic acid/ethyl acrylate copolymer P2 having an acidvalue of 290, the weight-average molecular weight of 5,000 and a glasstransition temperature of 77° C. was dissolved by use ofmonoethanolamine, the following anthraquinone-based Pigment Red-177dispersions D18 to D39 were made.

Materials Parts Copolymer P2 (15% by weight) 40 Pigment Red-177(manufactured by Ciba-Geigy) 24 Diethylene glycol 20 Isopropyl alcohol10 Water 130

These materials was added to the batch-type longitudinal sand milldevice (manufactured by AIMEX CO., LTD.) filled with glass beads, and adispersion treatment was continued for 3 hours during water cooling togive a crude dispersion with a viscosity of 30 cp and a pH of 9.8. Thisdispersion was centrifuged to remove large particles. Varying theconditions for centrifugation provided the dispersions D18 to D39 havingan average diameter ranging from 0.005 μm to 4 μm. Dilution of thesedispersions with water, diethylene glycol, and ethylene glycol monobutylether (60:25:15 by weight) gave red basic ink-jet inks R1 to R20 with aviscosity of 3 cp, a surface tension of 40 dyn/cm, and a pH of 9.5. Asolid content of a final ink was about 7.5% by weight. A final amount ofpigment in these inks was about 5% by weight. An average diameter of thepigment was determined by a particle size distribution measurementdevice (Otsuka Electronics Co., LTD.) using a dynamic light scatteringmethod. The average value was obtained from an initial gradient of anautocorrelation function.

In combinations of these inks R1 to R20 with the recording heads H5 toH7, examination of nozzle clogging occurrence was made to provide theresults as shown in Tables 6 to 8.

TABLE 6 In a case of the recording head H5 (t = 40 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) Dp/t(total nozzle number) Judgment R1 0.005 0.000125 1) X R2 0.01 0.00025 1)X R3 0.02 0.0005    0/128 ²⁾ ◯ R4 0.03 0.00075 0/128 ◯ R5 0.04 0.0010/128 ◯ R6 0.05 0.00125 0/128 ◯ R7 0.06 0.0015 0/128 ◯ R8 0.07 0.001750/128 ◯ R9 0.08 0.002 0/128 ◯ R10 0.09 0.00225 0/128 ◯ R11 0.1 0.00250/128 ◯ R12 0.15 0.00375 0/128 ◯ R13 0.2 0.005 0/128 ◯ R14 0.25 0.006250/128 ◯ R15 0.3 0.0075 0/128 ◯ R16 0.4 0.01 0/128 ◯ R17 1 0.025 30/128 Δ (partial clogging) R18 2 0.05 128/128  X (complete clogging) R19 30.075 128/128  X (complete clogging) R20 4 0.1 128/128  X (completeclogging) 1) No evaluation was performed due to ink instability. ²⁾ Aslight instability of the ink was observed.

TABLE 7 In a case of the recording head H6 (t = 50 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) Dp/t(total nozzle number) Judgment R1 0.005 0.0001 1) X R2 0.01 0.0002 1) XR3 0.02 0.0004 0/128 ◯ R4 0.03 0.0006 0/128 ◯ R5 0.04 0.0008 0/128 ◯ R60.05 0.001 0/128 ◯ R7 0.06 0.0012 0/128 ◯ R8 0.07 0.0014 0/128 ◯ R9 0.080.0016 0/128 ◯ R10 0.09 0.0018 0/128 ◯ R11 0.1 0.002 0/128 ◯ R12 0.150.003 0/128 ◯ R13 0.2 0.004 0/128 ◯ R14 0.25 0.005 0/128 ◯ R15 0.3 0.0060/128 ◯ R16 0.4 0.008 0/128 ◯ R17 1 0.02 36/128  Δ (partial clogging)R18 2 0.04 128/128  X (complete clogging) R19 3 0.06 128/128  X(complete clogging) R20 4 0.08 128/128  X (complete clogging) 1) Noevaluation was performed due to ink instability. ²⁾ A slight instabilityof the ink was observed.

TABLE 8 In a case of the recording head H7 (t = 60 μm) Pigment (Nozzlenumber subjected diameter to nozzle clogging)/ Ink D_(p) (μm) Dp/t(total nozzle number) Judgment R1 0.005 0.000083 1) X R2 0.010.000167 1) X R3 0.02 0.00033    0/128 ²⁾ ◯ R4 0.03 0.0005 0/128 ◯ R50.04 0.00067 01128 ◯ R6 0.05 0.000833 0/128 ◯ R7 0.06 0.001 0/128 ◯ R80.07 0.001167 0/128 ◯ R9 0.08 0.00133 0/128 ◯ R10 0.09 0.0015 0/128 ◯R11 0.1 0.00167 0/128 ◯ R12 0.15 0.0025 0/128 ◯ R13 0.2 0.0033 0/128 ◯R14 0.25 0.004167 0/128 ◯ R15 0.3 0.005 0/128 ◯ R16 0.4 0.0067 0/128 ◯R17 1 0.0167 48/128  Δ (partial clogging) R18 2 0.033 128/128  X(complete clogging) R19 3 0.05 128/128  X (complete clogging) R20 40.067 128/128  X (complete clogging) 1) No evaluation was performed dueto ink instability. ²⁾ A slight instability of the ink was observed.

From these results, a stable ink droplet ejection in the absence ofnozzle clogging was accomplished when the pigment diameter D_(p) and thenozzle thickness t satisfied a relationship D_(p)/t≦0.01.

Another feature of the present invention will be described as follows.As noted above, the color agent in the recording liquid is not dye whichis dissolved in water or the like but pigment which is dispersed inwater or the like. From the foregoing results, it was discovered that nonozzle clogging takes place within the range of the above relationshipbetween the pigment diameter and nozzle thickness. Furthermore, it isnecessary to deposit ink droplets onto a desired surface of the recordreceiving member with high accuracy as well as to eject ink dropletsstably, when the ink ejection is performed using pigment-based inks.

To study the relation between the nozzle thickness t associated withnozzle clogging and a distance L between a nozzle plane and a receivermedium, such as paper, the following experiment was carried out by useof the above-mentioned H5 to H7 which have an orifice diameter of φ25 μmand a nozzle number of 128 to give 400 dpi resolution. A size of theheating element was 22 μm×90 μm, its resistance value was 110 Ω, a drivevoltage of ink ejection was 24 V, a width of a drive pulse was 6.5 μsand a drive frequency was 12 kHz. Using the above red basic R5 as anink-jet ink and a matted coat NM (manufactured by Mitsubishi PaperMills) as a receiving member, a printing experiment was performed usingdistances L between the nozzle plate of the recording head and thereceiving medium. An evaluation as to whether a high-quality recording(a high dot positional precision) was achieved was made by examinationof a pixel positional precision on a surface of the receiving medium. Ina case in which the present apparatus employed the small nozzle and thepigment-based ink-jet ink, so that it was difficult to eject inkdroplets accurately as compared to a conventional apparatus, twoejection directions was evaluated in this experiment, so as to take intothe consideration the effect of gravity on ejection characteristics.That is, the ink was ejected both in a horizontal direction and verticaldirection. The results are shown in Table 9.

TABLE 9 Head H5 Head H6 Head H7 Distance (t = 40 μm) (t = 50 μm) (t = 60μm) L (mm) H¹⁾ V²⁾ H¹⁾ V²⁾ H¹⁾ V²⁾ 0.1 2.5t — — 2t — — 1.7t — — 0.512.5t ◯ ◯ 10t ◯ ◯ 8.3t ◯ ◯ 1 25t ◯ ◯ 20t ◯ ◯ 16.7t ◯ ◯ 1.5 37.5t ◯ ◯ 30t◯ ◯ 25t ◯ ◯ 2 50t ◯ ◯ 40t ◯ ◯ 33.3t ◯ ◯ 2.5 62.5t ◯ ◯ 50t ◯ ◯ 41.7t ◯ ◯3 75t ◯ ◯ 60t ◯ ◯ 50t ◯ ◯ 3.5 87.5t ◯ ◯ 70t ◯ ◯ 58.3t ◯ ◯ 4 100t Δ ◯ 80t◯ ◯ 66.7t ◯ ◯ 4.5 112.5t X ◯ 90t ◯ ◯ 75t ◯ ◯ 5 125t X X 100t Δ ◯ 83.3t ◯◯ 5.5 137.5t X X 110t X ◯ 91.7t ◯ ◯ 6 150t X X 120t X X 100t Δ ◯ 6.5162.5t X X 130t X X 108.3t X ◯ 7 175t X X 140t X X 125t X X 8 200t X X160t X X 133.3t X X ¹⁾H represents a horizontal direction. ²⁾Vrepresents a vertical direction.

In Table 9, mark ∘ indicates that a gap between a printed dot positionand a desired dot position is less than a quarter dot, mark Δ indicatesthat the gap is more than a quarter dot and less than a half dot, andmark X indicates that the gap is more than a half dot. A size of the dotwas approximately 60 μm diameter. From the results, even the presentapparatus which has the small nozzle and has difficulty in ejectingdroplets as compared to the conventional apparatus can eject inkdroplets stably to produce a high quality recording image with a highdot positional precision under conditions that the distance L betweenthe nozzle plane and the surface of the receiving member is less than100 t. Especially, it is preferred that the ejection direction bevertical to avoid a recording position change due to gravity. Thepresent invention is not necessarily limited by using a completelyvertical direction of droplet ejection, and is still effective under aslight influence of gravity. When using the present invention, it isadvantageous to eject droplets in a downward direction in a case of anabsence of a completely vertical ejection direction due to a structuralrestriction of the printer.

Next, another feature of the present invention will be described asfollows. As noted above, the present invention relates to the ink-jetrecording method wherein an ink droplet can be ejected from the smallorifice, and problems, such as damage and wear of the nozzle caused bythe pigments in the ink must be solved, because these problem havesignificant influences on ink drop ejection characteristics.

Recently, as mentioned above, to obtain a high-quality andhigh-resolution ink-jet image, a smaller nozzle has been required forthis purpose, although a conventional nozzle diameter from φ33˜φ34 μm(about 900 μm² in terms of cross-sectional area of the nozzle orifice)to φ50˜φ51 μm (about 2000 μm² in terms of cross-sectional area of thenozzle orifice) in the recording head has been used. In this case,although the previous relatively large nozzle is subjected to slightdamage and wear, there is little influence on ink drop ejectioncharacteristics, such as ejection stability, ink weight uniformity andthe like, thereby causing the damage and wear to be almost negligiblefor the size of nozzle. However in a case of the smaller nozzle having,for example, a less than φ25-μm diameter, even slight damage and wear ofthe nozzle have a significant influence on ink drop ejectioncharacteristics, such as ejection stability and ink weight uniformityand the like.

In the present invention, it was considered that the damage and wear ofthe nozzle may be prevented by the suitable choice of a hardness ofmaterials constituting a nozzle part. The following experiment focuseson a relation between the hardness of nozzle materials and damage andwear of the nozzle. More specifically, the nozzle plates of therecording head shown in FIG. 3A were made with various materialhardnesses. Evaluation as to whether nozzle damage and wear occurred andwhether deterioration of ink droplet ejection characteristics occurredwas performed. The ink-jet recording head based on thermal energy, whichrecording head was used in this experiment, is shown in FIG. 3B.Although FIG. 3B shows only four nozzles for simplicity, the actualnumber of nozzles used in this experiment was 128, thereby giving 400dpi resolution. Other conditions for recording were as follows. A sizeof the heating element was 22 μm×90 μm, its resistance value was 110Ω, adrive voltage of ink ejection was 24 V, a width of a drive pulse was 6.5μs, and a drive frequency was 12 kHz. Additionally, various nozzle partswere prepared by changing resins and metallic materials for the nozzleplate. The orifice diameters of φ25 μm (H8) and φ20 μm (H9) were used inthis experiment.

A comparative experiment was made with the orifice diameter of φ50 μm(reference head). In this case, number of nozzles used was 48, therebygiving 180 dpi resolution. A size of a heating element for this nozzlewas 40 μm×180 μm, its resistance value was 120Ω, a drive voltage for inkejection was 30 V, a width of a drive pulse was 7 μs, and a drivefrequency was 1.8 kHz. A thickness of each nozzle plate was 40 μm. Thehardness of various materials for the nozzle plate was evaluated by aRockwell hardness. An actual hardness was measured with a test piecesimilar to materials which form the nozzle plate. Table 10 shows theresults of the hardness of materials. The hardness is mainly expressedby a Rockwell M scale, but some metallic materials are expressed by aRockwell B scale. (The B scale is applied to harder materials than thatexhibiting M scale hardness.)

TABLE 10 Rockwell Sample Name of Materials Hardness S1 Silicone resin(filled with glass fiber) M45 S2 Vinylidene chloride resin M50 S3Polystyrene resin M65 S4 Polysulfone resin M69 S5 Polycarbonate resinM70 S6 Acrylonitrile-styrene copolymer M80 S7 Polymethyl methacrylateresin M90 S8 Allylic resin M95 S9 High-temperature cure-type epoxy resinM100 (curing agent: acid anhydrides)  S10 High-temperature cure-typeepoxy resin M108 (curing agent : aromatic amines)  S11 Urea resin(filled with α-cellulose) M120  S12 Aluminum M65  S13 Nickel B70 ¹⁾  S14Stainless (SUS304) B95 ¹⁾ ¹⁾ The B scale is higher than M140.

The ink used in this experiment was formed of the following compositionand by the following process. Examination was made using inks withdifferent pigment diameters ranging from 0.02 μm to 1 μm in combinationwith different diameters and different materials of the nozzle in therecording head.

The process for making the inks was as follows. Using a solution wherestyrene/acrylic acid/butyl methacrylate copolymer P3 having an acidvalue of 265, the weight-average molecular weight of 8,000 and a glasstransition temperature of 67° C. was dissolved by use ofmonoethanolamine, the following pigment red 122 dispersions D40 to D46were made.

Materials Parts Copolymer P3 (15% by weight) 40 Pigment Red 122(Fastgen-Hermagenta RT 24 manufactured by Dainippon Ink Chemical)Diethylene glycol 20 Isopropyl alcohol 10 Water 130

These materials was added to the batch-type longitudinal sand milldevice (manufactured by AIMEX Co., LTD.) filled with glass beads, and adispersion treatment was continued for 3 hours during water cooling togive a crude dispersion with a viscosity of 18 cp and a pH of 9.5. Thisdispersion was centrifuged to remove large particles. Varying theconditions for centrifugation provided the dispersions D40 to D46 havingan average diameter ranging from 0.02 μm to 1 μm. Dilution of thesedispersions with water, diethylene glycol and ethylene glycol monobutylether (60:30:10 by weight) gave magenta basic ink-jet inks M1 to M7 witha viscosity of 3.3 cp, a surface tension of 35 dyn/cm, and a pH of 9.3.A solid content of a final ink was about 7.5% by weight. A final contentof the pigment in these inks was 5% by weight. An average pigmentdiameter was determined by a particle size distribution measurementdevice (Otsuka Electronics Co., LTD.) using a dynamic light scatteringmethod. The average was obtained from an initial gradient of anautocorrelation function.

In combinations of these inks M1 to M7 with the above differentdiameters and different materials of the nozzles, all 128 nozzlesejected ink drops so that each nozzle could emit 5×10⁸ drops. Evaluationfor nozzle damage and wear between initial and final states of inkdroplet ejection was made to study deterioration of ink ejectioncharacteristics. The results are tabulated in Tables 11, 12, and 13. Inthese tables, mark ∘ indicates no observation of nozzle damage and wearand no deterioration of ink ejection characteristics, mark Δ indicatesslight nozzle damage and wear, but no deterioration of ink ejectioncharacteristics, and mark X indicates that the nozzle was damaged andworn and that ink ejection characteristics were deteriorated.

TABLE 11 In a case of H8 (orifice diameter was φ25 μm) M1 ink M2 ink M3ink M4 ink M5 ink M6 ink M7 ink Pigment Pigment Pigment Pigment PigmentPigment Pigment Sample diameter diameter diameter diameter diameterdiameter diameter No. 0.02 μm 0.05 μm 0.1 μm 0.2 μm 0.4 μm 0.6 μm 1 μmS1 ◯ X X X X X X S2 ◯ X X X X X X S3 ◯ ◯ ◯ ◯ X X X S4 ◯ ◯ ◯ ◯ X X X S5 ◯◯ ◯ ◯ X X X S6 ◯ ◯ ◯ ◯ X X X S7 ◯ ◯ ◯ ◯ X X X S8 ◯ ◯ ◯ ◯ X X X S9 ◯ ◯ ◯◯ X X X S10 ◯ ◯ ◯ ◯ X X X S11 ◯ ◯ ◯ ◯ X X X S12 ◯ ◯ ◯ ◯ X X X S13 ◯ ◯ ◯◯ ◯ ◯ X S14 ◯ ◯ ◯ ◯ ◯ ◯ X

TABLE 12 In a case of H9 (orifice diameter was φ20 μm) M1 ink M2 ink M3ink M4 ink M5 ink M6 ink M7 ink Pigment Pigment Pigment Pigment PigmentPigment Pigment Sample diameter diameter diameter diameter diameterdiameter diameter No. 0.02 μm 0.05 μm 0.1 μm 0.2 μm 0.4 μm 0.6 μm 1 μmS1 ◯ X X X X X X S2 ◯ X X X X X X S3 ◯ ◯ ◯ ◯ X X X S4 ◯ ◯ ◯ ◯ X X X S5 ◯◯ ◯ ◯ X X X S6 ◯ ◯ ◯ ◯ X X X S7 ◯ ◯ ◯ ◯ X X X S8 ◯ ◯ ◯ ◯ X X X S9 ◯ ◯ ◯◯ X X X S10 ◯ ◯ ◯ ◯ X X X S11 ◯ ◯ ◯ ◯ X X X S12 ◯ ◯ ◯ ◯ X X X S13 ◯ ◯ ◯◯ ◯ ◯ X S14 ◯ ◯ ◯ ◯ ◯ ◯ X

TABLE 13 Comparative reference (orifice diameter was φ50 μm) M1 ink M2ink M3 ink M4 ink M5 ink M6 ink M7 ink Pigment Pigment Pigment PigmentPigment Pigment Pigment Sample diameter diameter diameter diameterdiameter diameter diameter No. 0.02 μm 0.05 μm 0.1 μm 0.2 μm 0.4 μm 0.6μm 1 μm S1 ◯ X X X X X X S2 ◯ X X X X X X S3 ◯ ◯ ◯ ◯ Δ Δ Δ S4 ◯ ◯ ◯ ◯ ΔΔ Δ S5 ◯ ◯ ◯ ◯ Δ Δ Δ S6 ◯ ◯ ◯ ◯ Δ Δ Δ S7 ◯ ◯ ◯ ◯ Δ Δ Δ S8 ◯ ◯ ◯ ◯ Δ Δ ΔS9 ◯ ◯ ◯ ◯ Δ Δ Δ S10 ◯ ◯ ◯ ◯ Δ Δ Δ S11 ◯ ◯ ◯ ◯ Δ Δ Δ S12 ◯ ◯ ◯ ◯ Δ Δ ΔS13 ◯ ◯ ◯ ◯ ◯ ◯ Δ S14 ◯ ◯ ◯ ◯ ◯ ◯ Δ

From the results, it is understood that even though the recording headwith the large orifice diameter is subjected to slight damage and wear,deterioration of ink ejection characteristics is unlikely to occur. Inthe case of the small nozzle orifice diameter of less than φ25 μm in thepresent invention, it is understood that the requirement of the absenceof nozzle damage and wear must be selected to eject ink droplets stably,since the nozzle damage and wear cause ink droplet characteristics to bedeteriorated. When a form of the orifice is rectangular and trapezoidalinstead of the round orifice, the results are the same as for thepresent invention. In this case, the orifice diameter of less than φ25μm corresponds to the orifice cross-sectional area of about 500 μm² andthe present invention can be applied to the recording head having theorifice cross-sectional area of less than about 500 μm² instead of theround orifice.

More specifically, from Tables 11 and 12, the nozzle portion must beformed of resin materials which have a hardness of Rockwell M65 to M120in order to prevent nozzle damage and wear problems when using the inkhaving the pigment diameter ranging from 0.02 μm to 0.2 μm. However,nozzle damage and wear is unlikely to occur when using the ink havingthe pigment diameter of 0.02 μm in combination with the nozzle portionformed of materials which have a hardness of less than Rockwell M65,thereby causing the absence of deterioration of ink ejectioncharacteristics, but this is impractical because the ink used can belimited by the nozzle hardness.

Although the above discussions are described with regard to thebubble-jet recording method, the present invention is not limited tothis method. The present invention can be applied to all ink-jetrecording methods which employ a small nozzle orifice and pigment-basedink. Furthermore, it goes without saying that the present invention isapplicable to multicolor ink-jet recording, although the above examplesare described with use of a single ink.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from scope of the present invention.

The present application is based on Japanese priority application Nos.10-205195 filed on Jul. 21, 1998, 10-327734 filed on Nov. 18, 1998, and11-104494 filed on Apr. 12, 1999, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A liquid jet recording head for ejecting arecording composition from orifices toward a receiving medium so as toaccomplish a recording, said recording composition formed by dispersingfine particles, wherein: said orifices have a diameter equal to or lessthan 25 μm; and each of said fine particles has a size D_(p) determinedby a relationship 0.001≦D_(p)/D_(o)≦0.01 wherein D_(o) represents adiameter of said orifices.
 2. The head as claimed in claim 1, whereinsaid recording composition comprises a plurality of color recordingcompositions, each of said color recording compositions including saiddispersed fine particles corresponding to a respective color, theplurality of color recording compositions being ejectable from each ofsaid orifices corresponding to the respective color.
 3. The head asclaimed in claim 2, further comprising a plurality of recording headswhich eject the plurality of color recording compositions and form ahead unit.
 4. The head as claimed in claim 3, wherein said head unitincludes a nozzle part and a recording liquid reservoir part integrallyformed with the nozzle part.
 5. The head as claimed in claim 3, whereinsaid head unit includes a nozzle part and a recording liquid reservoirpart separable from the nozzle part.
 6. The head as claimed in claim 5,wherein said recording liquid reservoir part is separable according to akind of the recording composition.
 7. A liquid jet recording head forejecting a recording composition from orifices toward a receiving mediumso as to accomplish a recording, said recording composition formed bydispersing fine particles, wherein: said orifices have a diameter equalto or less than 25 μm; and a content of said fine particles in saidrecording composition is in the range of 2 to 10% by weight and a solidcontent of said recording composition including said fine particles isless than 15% by weight.
 8. The head as claimed in claim 7, wherein saidrecording composition comprises a plurality of color recordingcompositions, each of said color recording compositions including saiddispersed fine particles corresponding to a respective color, theplurality of color recording compositions being ejectable from each ofsaid orifices corresponding to the respective color.
 9. The head asclaimed in claim 8, further comprising a plurality of recording headswhich eject the plurality of color recording compositions and form ahead unit.
 10. The head as claimed in claim 9, wherein said head unitincludes a nozzle part and a recording liquid reservoir part integrallyformed with the nozzle part.
 11. The head as claimed in claim 9, whereinsaid head unit includes a nozzle part and a recording liquid reservoirpart separable from the nozzle part.
 12. The head as claimed in claim11, wherein said recording liquid reservoir part is separable accordingto a kind of the recording composition.
 13. A liquid jet recording headfor ejecting a recording composition from orifices toward a receivingmedium so as to accomplish a recording, fine particles having a sizeD_(p) being dispersed in said recording composition, each of saidorifices being a tip of a liquid passageway, wherein: said orifices havea diameter equal to or less than 25 μm; and D_(p) is determined by arelationship: D_(p)/t≦0.01 wherein t is a length of said orifices havinga uniform cross-sectional area at an outlet portion.
 14. The head asclaimed in claim 13, further comprising a nozzle plate having secondorifices communicating with liquid passageways.
 15. The head as claimedin claim 13, further comprising a plurality of recording heads whicheject the plurality of color recording compositions and form a headunit.
 16. The head as claimed in claim 15, wherein said head unitincludes a nozzle part and a recording liquid reservoir part integrallyformed with the nozzle part.
 17. The head as claimed in claim 15,wherein said head unit includes a nozzle part and a recording liquidreservoir part separable from the nozzle part.
 18. The head as claimedin claim 17, wherein said recording liquid reservoir part is separableaccording to a kind of the recording composition.
 19. A liquid jetrecording head for ejecting a recording composition from orifices towarda receiving medium so as to accomplish a recording, said recordingcomposition formed by dispersing fine particles, wherein: said orificesare formed of resin material and have a diameter equal to or less than25 μm; and said resin material has a hardness of Rockwell M65 to M120.20. The head as claimed in claim 19, wherein each of said fine particlesis a pigment having a diameter ranging from 0.02 μm to 0.2 μm.
 21. Thehead as claimed in claim 19, further comprising a plurality of recordingheads which eject the plurality of color recording compositions and forma head unit.
 22. The head as claimed in claim 21, wherein said head unitincludes a nozzle part and a recording liquid reservoir part integrallyformed with the nozzle part.
 23. The head as claimed in claim 21,wherein said head unit includes a nozzle part and a recording liquidreservoir part separable from the nozzle part.
 24. The head as claimedin claim 23, wherein said recording liquid reservoir part is separableaccording to a kind of the recording composition.
 25. A thermal inkjetrecording apparatus for ejecting a recording liquid from orifices towarda receiving medium so as to accomplish a recording by applying dropletsof the recording liquid to the receiving medium, said recording liquidformed by dispersing fine particles in a liquid, wherein: said orificeshave a diameter equal to or less than 25 μm; and each of said fineparticles has a size D_(p) determined by a relationship0.001≦D_(p)/D_(o)≦0.01 wherein D_(o) represents a diameter of saidorifices.
 26. The thermal inkjet recording apparatus as claimed in claim25, wherein said recording liquid comprises a plurality of colorrecording liquids, each of said color recording liquids including saiddispersed fine particles corresponding to a respective color, theplurality of color recording liquids being ejectable from each of saidorifices corresponding to the respective color.
 27. The thermal inkjetrecording apparatus as claimed in claim 25, further comprising aplurality of recording heads which eject a plurality of color recordingliquids and form a single piece head unit.
 28. The thermal inkjetrecording apparatus as claimed in claim 27, wherein said head unitincludes a nozzle part and recording liquid reservoir part integrallyformed with the nozzle part.
 29. The thermal inkjet recording apparatusas claimed in claim 27, wherein said head unit includes a nozzle partand a recording liquid reservoir part separable from the nozzle part.30. The thermal inkjet recording apparatus as claimed in claim 29,wherein said recording liquid reservoir part separable according to akind of the recording liquid.
 31. A thermal inkjet recording apparatusfor ejecting a recording liquid from orifices toward a receiving mediumso as to accomplish a recording by applying droplets of the recordingliquid to the receiving medium, said recording liquid formed bydispersing fine particles in a liquid, wherein: said orifices have adiameter equal to or less than 25 μm; and a content of said fineparticles in said recording liquid is in the range of 2 to 10% by weightand a solid content of said recording liquid including said fineparticles is less than 15% by weight.
 32. The thermal inkjet recordingapparatus as claimed in claim 31, wherein said recording liquidcomprises a plurality of color recording liquids, each of said colorrecording liquids including said dispersed fine particles correspondingto a respective color, the plurality of color recording liquids beingejectable from each of said orifices corresponding to the respectivecolor.
 33. The thermal inkjet recording apparatus as claimed in claim38, wherein a distance between said orifices and a surface of thereceiving medium is equal to or less than 100 t, and said recordingliquid is ejected from said orifices in a direction of gravityapproximately.
 34. The thermal inkjet recording apparatus as claimed inclaim 31, further comprising a plurality of recording heads which ejecta plurality of color recording liquids and form a single piece headunit.
 35. The thermal inkjet recording apparatus as claimed in claim 34,wherein said head unit includes a nozzle part and a recording liquidreservoir part integrally formed with the nozzle part.
 36. The thermalinkjet recording apparatus as claimed in claim 34, wherein said headunit includes a nozzle part and a recording liquid reservoir partseparable from the nozzle part.
 37. The thermal inkjet recordingapparatus as claimed in claim 36, wherein said recording liquidreservoir part is separable according to a kind of the recording liquid.38. A thermal inkjet recording apparatus for ejecting a recording liquidfrom orifices toward a receiving medium so as to accomplish a recordingby applying droplets of the recording liquid by applying droplets of therecording liquid to the receiving medium, fine particles having a sizeD_(p) being dispersed in said recording liquid, each of said orificesbeing a tip of liquid passageway or formed at an end of said passageway,wherein: said orifices have a diameter equal to or less than 25 μm; andD_(p) is determined by a relationship: D_(p)/t≦0.01 wherein t is alength of said orifices having a uniform cross-sectional area at anoutlet portion.
 39. The thermal inkjet recording apparatus as claimed inclaim 38, further comprising a plurality of recording heads which ejecta plurality of color recording liquids and form a single piece headunit.
 40. The thermal inkjet recording apparatus as claimed in claim 39,wherein said head unit includes a nozzle part and a recording liquidreservoir part integrally formed with the nozzle part.
 41. The thermalinkjet recording apparatus as claimed in claim 39, wherein said headunit includes a nozzle part and a recording liquid reservoir partseparable from the nozzle part.
 42. The thermal inkjet recordingapparatus as claimed in claim 44, wherein said recording liquidreservoir part is separable according to a kind of the recording liquid.43. A thermal inkjet recording apparatus for ejecting a recording liquidfrom orifices toward a receiving medium so as to accomplish a recordingby applying droplets of the recording liquid to the receiving medium,said recording liquid formed by dispersing fine particles in a liquid,wherein: said orifices are formed of resin material and have a diameterequal to or less than 25 μm; and said resin material has hardness ofRockwell M65 to M120.
 44. The thermal inkjet recording apparatus asclaimed in claim 43, wherein each of said fine particles is a pigmenthaving a diameter ranging from 0.02 μm to 0.2 μm.
 45. The thermal inkjetrecording apparatus as claimed in claim 43, further comprising aplurality of recording heads which eject a plurality of color recordingliquids and form a single piece head unit.
 46. The thermal inkjetrecording apparatus as claimed in claim 45, wherein said head unitincludes a nozzle part and a recording liquid reservoir part integrallyformed with the nozzle part.
 47. The thermal inkjet recording apparatusas claimed in claim 45, wherein said head unit includes a nozzle partand a recording liquid reservoir part separable from the nozzle part.48. The thermal inkjet recording apparatus as claimed in claim 47,wherein said recording liquid reservoir part is separable according to akind of the recording liquid.
 49. A thermal inkjet recording head forejecting a recording liquid from orifices toward a receiving medium soas to accomplish a recording by applying droplets of the recordingliquid to the receiving medium, said recording liquid formed bydispersing fine particles in a liquid, wherein: said orifices have adiameter equal to or less than 25 μm; and each of said fine particleshas a size D_(p) determined by a relationship 0.001≦D_(p)/D_(o)≦0.01wherein D_(o) represents a diameter of said orifices.
 50. The thermalinkjet recording head as claimed in claim 49, wherein said recordingliquid comprises a plurality of color recording liquids, each of saidcolor recording liquids including said dispersed fine particlescorresponding to a respective color, the plurality of color recordingliquids being ejectable from each of said orifices corresponding to therespective color.
 51. The thermal inkjet recording head as claimed inclaim 49, further comprising a plurality of recording heads which ejecta plurality of color recording liquids and form a single piece headunit.
 52. The thermal inkjet recording head as claimed in claim 51,wherein said head unit includes a nozzle part and recording liquidreservoir part integrally formed with the nozzle part.
 53. The thermalinkjet recording head as claimed in claim 51, wherein said head unitincludes a nozzle part and a recording liquid reservoir part separablefrom the nozzle part.
 54. The thermal inkjet recording head as claimedin claim 53, wherein said recording liquid reservoir part separableaccording to a kind of the recording liquid.
 55. A thermal inkjetrecording head for ejecting a recording liquid from orifices toward areceiving medium so as to accomplish a recording by applying droplets ofthe recording liquid to the receiving medium, said recording liquidformed by dispersing fine particles in a liquid, wherein: said orificeshave a diameter equal to or less than 25 μm; and a content of said fineparticles in said recording liquid is in the range of 2 to 10% by weightand a solid content of said recording liquid including said fineparticles is less than 15% by weight.
 56. The thermal inkjet recordinghead as claimed in claim 55, wherein said recording liquid comprises aplurality of color recording liquids, each of said color recordingliquids including said dispersed fine particles corresponding to arespective color, the plurality of color recording liquids beingejectable from each of said orifices corresponding to the respectivecolor.
 57. The thermal inkjet recording head as claimed in claim 62,wherein a distance between said orifices and a surface of the receivingmedium is equal to or less than 100 t, and said recording liquid isejected from said orifices in a direction of gravity approximately. 58.The thermal inkjet recording head as claimed in claim 55, furthercomprising a plurality of recording heads which eject a plurality ofcolor recording liquids and form a single piece head unit.
 59. Thethermal inkjet recording head as claimed in claim 58, wherein said headunit includes a nozzle part and a recording liquid reservoir partintegrally formed with the nozzle part.
 60. The thermal inkjet recordinghead as claimed in claim 58, wherein said head unit includes a nozzlepart and a recording liquid reservoir part separable from the nozzlepart.
 61. The thermal inkjet recording head as claimed in claim 60,wherein said recording liquid reservoir part is separable according to akind of the recording liquid.
 62. A thermal inkjet recording head forejecting a recording liquid from orifices toward a receiving medium soas to accomplish a recording by applying droplets of the recordingliquid by applying droplets of the recording liquid to the receivingmedium, fine particles having a size D_(p) being dispersed in saidrecording liquid, each of said orifices being a tip of liquid passagewayor formed at an end of said passageway, wherein: said orifices have adiameter equal to or less than 25 μm; and D_(p) is determined by arelationship: D_(p)/t≦0.01 wherein t is a length of said orifices havinga uniform cross-sectional area at an outlet portion.
 63. The thermalinkjet recording head as claimed in claim 62, further comprising aplurality of recording heads which eject a plurality of color recordingliquids and form a single piece head unit.
 64. The thermal inkjetrecording head as claimed in claim 63, wherein said head unit includes anozzle part and a recording liquid reservoir part integrally formed withthe nozzle part.
 65. The thermal inkjet recording head as claimed inclaim 63, wherein said head unit includes a nozzle part and a recordingliquid reservoir part separable from the nozzle part.
 66. The thermalinkjet recording head as claimed in claim 65, wherein said recordingliquid reservoir part is separable according to a kind of the recordingliquid.
 67. A thermal inkjet recording head for ejecting a recordingliquid from orifices toward a receiving medium so as to accomplish arecording by applying droplets of the recording liquid to the receivingmedium, said recording liquid formed by dispersing fine particles in aliquid, wherein: said orifices are formed of resin material and have adiameter equal to or less than 25 μm; and said resin material hashardness of Rockwell M65 to M120.
 68. The thermal inkjet recording headas claimed in claim 67, wherein each of said fine particles is a pigmenthaving a diameter ranging from 0.02 μm to 0.2 μm.
 69. The thermal inkjetrecording head as claimed in claim 67, further comprising a plurality ofrecording heads which eject a plurality of color recording liquids andform a single piece head unit.
 70. The thermal inkjet recording head asclaimed in claim 69, wherein said head unit includes a nozzle part and arecording liquid reservoir part integrally formed with the nozzle part.71. The thermal inkjet recording head as claimed in claim 69, whereinsaid head unit includes a nozzle part and a recording liquid reservoirpart separable from the nozzle part.
 72. The thermal inkjet recordinghead as claimed in claim 71, wherein said recording liquid reservoirpart is separable according to a kind of the recording liquid.